[en] The authors report on a simulation of the earth's magnetosphere interacting with the interplanetary magnetic field (IMF), studied on a global scale. Questions such as the response time of the magnetosphere to changes in the solar wind orientation, or explanations for the origin of magnetospheric substorms have to be addressed on global rather than local scales. Several theories have produced promising results for explaining the interaction of the solar wind and the magnetosphere, and recent data analyses of ISEE 1 and 2 data have provided more information bearing on this issue. The authors ask two main questions: first, how does the magnetospheric response change with northward vs southward orientation of the IMF; and second, how do the northward or southward components of the IMF impact on magnetic reconnection processes in the plasma sheet? This computerized simulation uses a model and code previously developed, and studies the questions in the framework of resistive MHD equations. The authors conclude that a southward IMF does reconnect along the dayside magnetopause, and the initiation of this reconnection serves to induce plasma sheet reconnection. As a consequence plasmoids are formed in the magnetotail, and accelerated both earthward and tailward. A northward IMF acts to stop plasma sheet reconnection, by removing magnetic flux from the outer part of the magnetosphere, which decreases cross-tail currents, inhibiting plasma sheet reconnection. Magnetic pressure effects due to the presence of a northward IMF also cause the shape of the magnetosphere to change from its more normal cometlike tail to something resembling a tadpole